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| United States Patent |
6,112,689
|
|
Baudet
|
September 5, 2000
|
Sail body and method for making
Abstract
A sail body (3) includes first and second skin layers (40, 42), each skin
layer having an outer film (22) at an outer side (34) and reinforcement
elements (28, 30) at an inner side (36). The skin layers are laminated
with the inner sides abutting to form the sail body. The skin layers are
each made up of skin components (38) joined to other skin components of
the same skin layer another along their aligned edges (43). The joined
edges (44) of the first skin layer are offset from the joined edges of the
second skin layer to strengthen the sail body. The sail body is preferably
a three-dimensional molded sail body. The fibers or other reinforcement
elements are preferable generally aligned with the expected load lines
(32) of the sail body.
| Inventors:
|
Baudet; Jean-Pierre (Emeryville, CA)
|
| Assignee:
|
Clear Image Concepts LLC (Alameda, CA)
|
| Appl. No.:
|
340276 |
| Filed:
|
June 25, 1999 |
| Current U.S. Class: |
114/102.33; 114/102.31 |
| Intern'l Class: |
B63H 009/04 |
| Field of Search: |
114/102.1,102.29,102.31,102.33
428/110,111
|
References Cited
U.S. Patent Documents
| 2565219 | Aug., 1951 | Gardiner et al.
| |
| 3903826 | Sep., 1975 | Andersen.
| |
| 3954076 | May., 1976 | Fracker.
| |
| 4444822 | Apr., 1984 | Doyle et al.
| |
| 4499842 | Feb., 1985 | Mahr.
| |
| 4554205 | Nov., 1985 | Mahr.
| |
| 4590121 | May., 1986 | Mahr.
| |
| 4593639 | Jun., 1986 | Conrad.
| |
| 4624205 | Nov., 1986 | Conrad.
| |
| 4679519 | Jul., 1987 | Linville.
| |
| 4708080 | Nov., 1987 | Conrad.
| |
| 4831953 | May., 1989 | Conrad.
| |
| 4945848 | Aug., 1990 | Linville.
| |
| 5001003 | Mar., 1991 | Mahr.
| |
| 5038700 | Aug., 1991 | Conrad.
| |
| 5097783 | Mar., 1992 | Linville.
| |
| 5097784 | Mar., 1992 | Baudet.
| |
| 5172647 | Dec., 1992 | Towne.
| |
| 5304414 | Apr., 1994 | Bainbridge et al.
| |
| 5333568 | Aug., 1994 | Meldner et al.
| |
| 5352311 | Oct., 1994 | Quigley.
| |
| 5355820 | Oct., 1994 | Conrad et al.
| |
| 5403641 | Apr., 1995 | Linville et al.
| |
| 5470632 | Nov., 1995 | Meldner et al.
| |
| Foreign Patent Documents |
| 056 657 | Jul., 1982 | EP.
| |
| 224 729 | Jun., 1987 | EP.
| |
| 281 322 | Sep., 1988 | EP.
| |
| 29 26 476 | Jun., 1979 | DE.
| |
| 31 19 734 | May., 1981 | DE.
| |
| WO 87/07233 | Dec., 1987 | WO.
| |
Other References
J.L. Kardos, "Short-Fiber-Reinforced Polymeric composites,
Structure-Porperty Relations," pp. 130-135.
"Consolidation Mechanisms and Interfacial Phenomena in Thermoplastic Powder
Impregnated Composites," Section 2.2.1. Tow spreading unit, four pages.
Catalog No. 5, Tools and Hardware for Manufacturing Composite Parts and
Laminates of All Types, Torr Technologies, Inc., Auburn, Washington.
|
Primary Examiner: Le; Mark T.
Assistant Examiner: Muldoon; Patrick Craig
Attorney, Agent or Firm: Townsend and Townsend and Crew LLP
Claims
What is claimed is:
1. A sail body comprising:
first and second skin layers, each said skin layer comprising an outer side
an inner side, an outer film at the outer side and reinforcement elements,
said inner sides abutting, said skin layers laminated to one another to
form a sail body;
said first and second skin layers each comprising skin components, said
skin components each comprising edges, said skin components of said first
skin layer joined to one another along their edges to create joined edges,
and said skin components of said second skin layer joined to one another
along their edges to create joined edges; and
the joined edges of said first skin layer being offset from the joined
edges of said second skin layer so that reinforcement elements of the
first and second skin layers cross over the joined edges of the second and
first skin layers, respectively.
2. The sail body according to claim 1 wherein said sail body is a molded
sail body with a three-dimensional contour.
3. The sail body according to claim 1 wherein said outer film of at least
one said skin layer is imperforate.
4. The sail body according to claim 1 wherein said outer films are made of
the same film material.
5. The sail body according to claim 1 wherein said reinforcement elements
of at least one said skin component comprise a first set of generally
parallel reinforcement elements.
6. The sail body according to claim 1 wherein said reinforcement elements
of said at least one said skin component comprises a second set of
generally parallel reinforcement elements oriented transversely to said
first set of generally parallel reinforcement elements.
7. The sail body according to claim 1 wherein said sail body has expected
load lines and said first set of generally parallel reinforcement elements
are generally aligned with said expected load lines.
8. The sail body according to claim 1 wherein said reinforcement elements
comprise twisted and untwisted multifiber yarns.
9. The sail body according to claim 1 wherein said reinforcement elements
are at the inner side.
10. The sail body according to claim 1 wherein said reinforcement elements
comprise fiberous scrim.
11. The sail body according to claim 10 wherein said scrim is a woven
scrim.
12. A sail body comprising:
first and second skin layers, each said skin layer comprising an outer film
at an outer, film side and reinforcement elements at an inner,
reinforcement side, said reinforcement sides abutting, said skin layers
adhered to one another to form a molded sail body with a three-dimensional
contour;
said first and second skin layers each comprising skin components having
edges, the skin components of the first skin layer joined to one another
along their edges to create joined edges, the skin components of the
second skin layer joined to one another along their edges to create joined
edges;
said outer film of at least one said skin layer being imperforate;
said reinforcement elements of at least one said skin component comprising
a first set of generally parallel reinforcement elements and a second set
of generally parallel reinforcement elements oriented transversely to said
first set of generally parallel reinforcement elements;
said sail body having expected load lines, said first set of generally
parallel reinforcement elements being generally aligned with said expected
load lines; and
the joined edges of said first skin layer being offset from the joined
edges of said second skin layer.
13. A method for making a sail body comprising:
creating a set of first skin components and a set of second skin
components, said skin components each having edges;
joining the set of first skin components along edges thereof to create a
first skin layer with joined edges;
joining the set of second skin components along edges thereof to create a
second skin layer with joined edges, each said skin layer comprising an
outer side, and inner side, an outer film at the outer side, and
reinforcement elements;
laminating said first and second skin layers with the inner sides abutting
to create a sail body; and
offsetting, prior to the laminating step, the joined edges of the first and
second skin layers of the sail body so that reinforcement elements of the
first and second skin layers cross over the joined edges of the second and
first skin layers, respectively.
14. The method according to claim 13 wherein the skin components creating
step comprises:
obtaining reinforced film made from a length of film, a reinforcement web
and an uncured adhesive; and
severing the reinforced film to create the sets of first and second skin
components.
15. The method according to claim 13 wherein said joining steps are carried
out by temporarily securing said sets of first and second skin components
along their respective joined edges to permit shifting of the skin
components during said adhering step.
16. The method according to claim 15 wherein said laminating step is
carried out using heat and pressure.
17. The method according to claim 16 wherein said laminating step is
carried out using a three-dimensional mold to create a three-dimensional
sail body.
18. The method according to claim 13 wherein said offsetting step is
carried out in the creating and joining steps in which the first and
second skin layers are effectively congruent.
19. The method according to claim 13 wherein the creating step is carried
out by severing a reinforced film to create the sets of first and second
skin components, the first and second skin components each comprising
generally parallel first reinforcement elements.
20. The method according to claim 19 further comprising determining a set
of expected load lines for the sail body and generally aligning the first
reinforcement elements with the expected load lines.
21. The method according to claim 20 wherein the creating step is carried
out using a reinforced film comprising second reinforcement elements
oriented transverse to the first reinforced elements.
22. A method for making a sail body comprising:
forming reinforced film by laminating a length of film, a web of
reinforcement elements and an uncured adhesive;
severing the reinforced film to create sets of first and second skin
components, the skin components each having edges;
joining the set of first skin components along their edges to create a
first skin layer with joined edges;
joining the set of second skin components along their edges to create a
second skin layer with joined edges, each said skin layer comprising an
outer side, an inner side, an outer film at the outer side, and
reinforcement elements at the inner side;
laminating said first and second skin layers in a three-dimensional mold
using heat and pressure with the inner sides abutting to create a
three-dimensional sail body;
said joining steps being carried out by temporarily securing said sets of
first and second skin components along their respective edges to permit
shifting of the skin components during said laminating step; and
offsetting, prior to the adhering step, the joined edges of the first and
second skin layers of the sail body so that reinforcement elements of the
first and second skin layers cross over the joined edges of the second and
first skin layers, respectively.
Description
BACKGROUND OF THE INVENTION
The present invention is directed to the field of sails, methods for their
manufacture and apparatus used in their manufacture.
Sails can be flat, two-dimensional sails or three-dimensional sails. Most
typically, three-dimensional sails are made by broadseaming a number of
panels. The panels, each being a finished piece of sailcloth, are cut
along a curve and assembled to other panels to create the
three-dimensional aspect for the sail. The panels typically have a
quadrilateral or triangular shape with a maximum width being limited
traditionally by the width of the roll of finished sailcloth from which
they are being cut. Typically the widths of the sailcloth rolls range
between about 91.5 and 137 centimeters (36 and 58 inches).
Sail makers have many restraints and conditions placed on them. In addition
to building products which will resist deterioration from weather and
chafe abuses, a goal of modern sailmaking is to create a lightweight,
flexible, three-dimensional air foil that will maintain its desired
aerodynamic shape through a chosen wind range. A key factor in achieving
this goal is stretch control of the airfoil. Stretch is to be avoided for
two main reasons. First, it distorts the sail shape as the wind increases,
making the sail deeper and moving the draft aft. This creates undesired
drag as well as excessive heeling of the boat. Second, sail stretch wastes
precious wind energy that should be transferred to the sailcraft through
its rigging.
Over the years, sailmakers have attempted to control stretch and the
resulting undesired distortion of the sail in three basic ways.
The first way sailmakers attempted to control sail stretch is by using
low-stretch high modulus yarns in the making of the sailcloth. The
specific tensile modulus in gr/denier is about 30 for cotton yarns (used
in the 1940's), about 100 for Dacron.RTM. polyester yarns from DuPont(used
in the 1950's to 1970's), about 900 for Kevlar.RTM. para-aramid yarns from
DuPont (used in 1980's) and about 3000 for carbon yarns (used in 1990's).
The second basic way sailmakers have attempted to control sail stretch has
involved better yarn alignment based on better understanding of stress
distribution in the finished sail. Lighter and yet lower-stretch sails
have been made by optimizing sailcloth weight and strength and working on
yarn alignment to match more accurately the encountered stress intensities
and their directions. The efforts have included both fill-oriented and
warp-oriented sailcloths and individual yarns sandwiched between two
films. With better understanding of the stress distribution, sailmaking
has evolved towards more sophisticated panel-layout constructions. Up
until the late 1970's, sails were principally made out of narrow panels of
fill-oriented woven sailcloth arranged in cross-cut construction where the
majority of the loads were crossing the seams and the width of the narrow
panels. With the appearance of high-performance yarn material, like
Kevlar, stretch of the numerous horizontal seams in the sails became a
problem. To solve this and to better match the yarn alignment with the
load patterns, an approach since the early 1980's has been to arrange and
seam narrow panels of warp-oriented sailcloths in panel-layout
constructions known as "Leech-cut" and later more successfully in the
"Tri-radial" construction. The "Tri-radial" construction is typically
broken into several sections made from narrow pre-assembled radiating
panels. The highly loaded sections of the sail such as the clew, the head
and the leech sections are typically made with radial panels cut from
heavy sailcloth. The less loaded sail sections, such as the luff and the
tack sections, are made with panels cut from lighter sailcloth. This
approach, unfortunately, has its own drawbacks. Large sails made this way
can have up to, for example, 120 narrow panels which must be cut and
broadseamed to each other with great precision to form the several large
sections. These large sections of pre-assembled panels are then joined
together to form the sail. This is extremely time-consuming, and thus
expensive, and any lack of precision often results in sail-shape
irregularities. The mix of types of sailcloths used causes the different
panels to shrink at different rates affecting the smoothness of the sail
along the joining seams of the different sections, especially over time.
An approach to control sail-stretch has been to build a more traditional
sail out of conventional woven fill-oriented sailcloth panels and to
reinforce it externally by applying flat tapes on top of the panels
following the anticipated load lines. See U.S. Pat. No. 4,593,639. While
this approach is relatively inexpensive, it has its own drawbacks. The
reinforcing tapes can shrink faster than the sailcloth between the tapes
resulting in severe shape irregularities. The unsupported sailcloth
between the tapes often bulges, affecting the design of the airfoil.
A further approach has been to manufacture narrow cross-cut panels of
sailcloth having individual laid-up yarns following the load lines. The
individual yarns are sandwiched between two films and are continuous
within each panel. See U.S. Pat. No. 4,708,080 to Conrad. Because the
individual radiating yarns are continuous within each panel, there is a
fixed relationship between yarn trajectories and the yarn densities
achieved. This makes it difficult to optimize yarn densities within each
panel. Due to the limited width of the panels, the problem of having a
large number of horizontal seams is inherent to this cross-cut approach.
The narrow cross-cut panels of sailcloth made from individual spaced-apart
radiating yarns are difficult to seam successfully; the stitching does not
hold on the individual yarns. Even when the seams are secured together by
adhesive to minimize the stitching, the proximity of horizontal seams to
the highly loaded corners can be a source of seam, and thus sail, failure.
A still further approach has been to manufacture simultaneously the
sailcloth and the sail in one piece on a convex mold using uninterrupted
load-bearing yarns laminated between two films, the yarns following the
anticipated load lines. See U.S. Pat. No. 5,097,784 to Baudet. While
providing very light and low-stretch sails, this method has its own
technical and economic drawbacks. The uninterrupted nature of every yarn
makes it difficult to optimize yarn densities, especially at the sail
corners. Also, the specialized nature of the equipment needed for each
individual sail makes this a somewhat capital-intensive and thus expensive
way to manufacture sails.
The third basic way sailmakers have controlled stretch and maintained
proper sail shape has been to reduce the crimp or geometrical stretch of
the yarn used in the sailcloths. Crimp is usually considered to be due to
a serpentine path taken by a yarn in the sailcloth. In a weave, for
instance, the fill and warp yarns are going up and down around each other.
This prevents them from being straight and thus from initially fully
resisting stretching. When the woven sailcloth is loaded, the yarns tend
to straighten before they can begin resist stretching based on their
tensile strength and resistance to elongation. Crimp therefore delays and
reduces the stretch resistance of the yarns at the time of the loading of
the sailcloth.
In an effort to eliminate the problems of this "weave-crimp", much work has
been done to depart from using woven sailcloths. In most cases, woven
sailcloths have been replaced by composite sailcloths, typically made up
from individual laid-up (non-woven) load-bearing yarns sandwiched between
two films of Mylar.RTM. polyester film from DuPont or some other suitable
film. There are a number of patents in this area, such as Sparkman EP 0
224 729, Linville U.S. Pat. No. 4,679,519, Conrad U.S. Pat. No. 4,708,080,
Linville U.S. Pat. No. 4,945,848, Baudet U.S. Pat. No. 5,097,784, Meldner
U.S. Pat. No. 5,333,568, and Linville U.S. Pat. No. 5,403,641.
Crimp, however, is not limited to woven sailcloth and can occur with
laid-up constructions also. Crimp in sailcloth made of laid-up yarn can be
created in several different ways. First, lateral shrinkage of the films
during many conventional lamination processes induces crimp into the
yarns. For example, with narrow crosscut panel construction, where a
majority of load-bearing yarns are crossing the panel widths, significant
crimp of these yarns is induced during lamination of the sailcloth between
high-pressure heated rolls. This is because the heated film shrinks
laterally as it undergoes thermoforming, typically about 2.5% with this
lamination method. The result is catastrophic with regard to the stretch
performance for the composite fabric in highly loaded applications.
Second, uninterrupted load-bearing yarns within a sail follow curved
trajectories. The yarns used are typically multifiber yarns. Twist is
generally added so that the fibers work together and resist stretch along
the curved trajectories. If no twist were added, only a few fibers would
be submitted to the loads, that is the ones on the outside of the curve.
This would substantially limit the ability of the sail to resist stretch.
While the tiny yarn spirals created using the twisted multi-fiber yarns
help increase load sharing amongst the fibers and therefore reduce
stretch, there is still crimp induced as the spiraled yarns straighten
under the loads. The twist in the yarns is therefore a necessary
compromise for this design, preventing however this type of sailcloth from
obtaining the maximum possible modulus from the yarns used.
The various approaches shown in Linville's patents are other attempts to
reduce crimp problems. Layers of continuous parallel spaced-apart laid-up
yarns are used to reinforce laminated sailcloth. However, because the
continuous spaced-apart yarns are parallel to each other, only a small
number of them are aligned with the loads. Panels cut out of these
sailcloths therefore have poor shear resistance. In addition, no change of
yarn density is achieved along the yarns direction. Therefore the proposed
designs do not offer constant strain qualities. In addition, these
approaches are designed to be used with panel-layout like the Cross-cut,
Leech-cut and Tri-radial constructions, which result in their own sets of
drawbacks.
The sailcloth shown in Meldner's patent may, in theory, reduce crimp
problems. However, it is designed to be used in Tri-radial construction,
which results in its own set of problems. Meldner laminates between two
films continuous layers of unidirectional unitapes made from side-by-side
pull-truded tows of filaments with diameters five times less than
conventional yarns. The continuous unidirectional layers are crossing-over
each other to increase filament-over-filament cross-over density, which is
believed to minimize crimp problems and increase shear strength. Meldner
is limited to the use of very small high performance yarns, which are
expensive. The cost of those yarns affects greatly the economics of this
approach and limits it to "Grand Prix" racing applications. In addition,
this design of sailcloth is not intended to offer constant strain
qualities; rather stretch and strength resistance are designed to be the
same throughout the entire roll length of the sailcloth. Only a small
number of the continuous unidirectional filaments end up aligned with the
loads.
U.S. patebt application Ser. No. 09/173,917 filed Oct. 16, 1998 and
entitled Composite Products, Methods and Apparatus, describes a low
stretch, flexible composite particularly useful for making high
performance sails. The composite includes first and second polymer films
with discontinuous, stretch resistant segments therebetween. The segments
extend generally along the expected load lines for the sail. The segments
have lengths which are substantially shorter than the corresponding
lengths of the load lines within each sail section. The sail can be either
two-dimensional or three dimensional. The two-dimensional sails can be
made from one section or a number of flat sections seamed together. Three
dimensional sails can be made using one or more molded sections of the
composite sheet or several flat sections can be broad seamed together to
create the three dimensional sail. The sail can be designed to exhibit
generally constant strain qualities under a desired use condition and to
permit low stretch performance to be optimized by minimizing the crimp,
that is the geometrical stretch, of the yarns.
SUMMARY OF THE INVENTION
The present invention is directed to a sail body and a method for making a
sail body which is particularly useful for making molded sails while
minimizing production steps and labor. The invention is especially well
suited for sails for smaller boats, such as 14 to 35 foot (4.3 to 10.7
meter) boats, where encountered loads are may not be excessive and where
constant strain characteristics may not be crucial.
A sail body made according to the invention includes first and second skin
layers, each skin layer having an outer film at an outer side and
reinforcement elements; the reinforcement elements may be at an inner side
of the skin layer. The inner sides of the first and second skin layers
abut one another; the skin layers are laminated to one another at their
inner sides to form the sail body. The skin layers are each made up of
skin components joined to other skin components of the same skin layer
along their edges. The joined edges of the first skin layer are offset
from the joined edges of the second skin layer to strengthen the sail
body.
The sail body may be a two-dimensional or a three-dimensional sail body.
The fibers or other reinforcement elements are preferable generally
aligned with the expected load lines of the sail body.
Another aspect of the invention is a method for making a sail body in which
sets of first and second skin components are created. The set of first
skin components are joined along their edges to create a first skin layer
and the set of second skin components are joined along their edges to
create a second skin layer. Each skin layer has an outer film and at an
outer side and preferably has reinforcement elements at an inner side. The
first and second skin layers are adhered to one another with the inner
sides abutting to create a sail body. The joined edges of the first and
second skin layers are offset so that reinforcement elements of the first
and second skin layers cross over the joined edges of the second and first
skin layers, respectively.
The joining steps are preferably carried out by temporarily securing the
first and second skin components along their respective joined edges to
permit shifting of the skin components during the adhering step. This
facilitates manufacture of three-dimensional molded sails.
Other features and advantages of the invention will appear from the
following description in which the preferred embodiments have been set
forth in detail in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a sail made according to the present invention
with an exemplary set of expected load lines shown in dashed lines;
FIG. 2 schematically illustrates manufacture of reinforced film;
FIG. 3 illustrates cutting skin components from the reinforced film of FIG.
2;
FIG. 4A illustrates a first skin layer created by temporarily joining a set
of appropriately shaped first skin components along their adjacent edges;
FIG. 4B illustrates a second skin layer made of a set of second skin
components joined along their adjacent edges;
FIG. 4C illustrates how the joined edges of the first and second skin
layers of FIGS. 4A and 4B are offset when the skin layers are placed one
on top of the other;
FIG. 5 suggests placing the second skin layer on top of the first skin
layer, the first skin layer on a flexible pressure sheet, the flexible
pressure sheet supported by a convex mold element;
FIG. 6 is a simplified end view illustrating placement of the stack of skin
layers between two high-friction, flexible pressure sheets stretched
between frames, the frames carried by upper and lower enclosure members,
with a three-dimensional mold element used to create a molded sail body;
FIG. 6A shows the structure of FIG. 6 after the upper and lower enclosure
members have been brought together, capturing the stack of material within
a lamination interior between the flexible pressure sheets, and placement
of first and second end enclosure members adjacent to the open ends of the
closed upper and lower enclosure members, each including a recirculating
fan and an electric heater element so to cause heated, circulating fluid
to pass by the outer surfaces of the flexible pressure sheets, and then
application of pressure to the outer surfaces of the flexible pressure
sheets by creating a partial vacuum within the lamination interior;
FIG. 6B is a simplified view taken along line 6B--6B of FIG. 6A; and
FIG. 7 illustrates a molded sail body taken from the three-dimensional mold
of FIG. 6.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
FIG. 1 illustrates a sail 2 made according to the invention. In this
embodiment sail 2 includes a sail body 3 and has three edges, luff 4,
leech 6 and foot 8. Sail 2 also has three corners, head 10 at the top,
tack 12 at the lower forward corner of the sail at the intersection of
luff 4 and foot 8, and clew 14 a the lower aft corner of the sail at the
intersection of the leech and the foot. While sail 2 is typically a
molded, generally triangular, three-dimensional sail, it could also be a
two-dimensional sail and could have any of a variety of shapes. The
finished sail 2 includes gussets 16 at head 10, tack 12 and clew 14 and
selvage 18 along luff 4, leech 6 and foot 8 to create the finished sail. A
process suitable for making sail body 3 and its construction will now be
discussed.
FIG. 2 illustrates making an uncured reinforced film 20 from an imperforate
film 22, typically made of PET or polyester film, an uncured adhesive web
24, such as a copolyester resin, or and a mesh or scrim of fibers or other
reinforcement elements 26. Film 22 could be made from other materials,
such as Kapton.RTM. polyimide film made by DuPont. The mesh or scrim will
typically be unwoven but may be woven for increased tear resistance. Mesh
or scrim 26 preferably includes a set of first reinforcement elements 28
which run parallel to one another along the length of film 20 and a set of
second, generally parallel reinforcement elements 30 which are arranged
transversely to, typically perpendicular to, reinforcement elements 28.
Reinforcement elements 28, 30 can be made from a variety of materials such
as monofilament material, multifiber yarns made of, for example, carbon
fiber, aramid fiber, polyester fiber or fiber sold under the trademarks
PBO.RTM., Pentex.RTM. or Spectra.RTM.. Reinforcement elements may be, for
example, cylindrical or flattened in cross-section and may be made of
twisted or untwisted fibers. Reinforcement elements 28 are typically, but
need not be, the fibers used to be generally aligned with the expected
load lines 32 of sail 2.
In one embodiment, first and second reinforcement elements 28, 30 are made
of 500 denier untwisted multifiber yarns and twisted multifiber yarns,
respectively. Second reinforcement elements 30 are preferably twisted
multifiber yarns for increased tear resistance. The spacing between first
reinforcement elements 28 is about 3 mm and the spacing between second
reinforcements elements is about 10 mm. However, the first and second
reinforcement elements 28, 30 could be made of different materials and
could be made with the same or different diameters. Also, the
reinforcement elements could have equal or unequal lateral spacing as
well. The choice of reinforcement elements 28, 30, their orientation and
their spacing will be determined in large part by the expected loading of
sail 2.
Reinforced film 20 has an outer, film side 34 and inner, reinforcement side
36. Film 20 is cut into skin components 38 of various shapes and sizes as
suggested in FIG. 3. Skin components 38 are joined together to create the
first and second skin layers 40, 42. First and second skin layers 40, 42
are each created by temporarily securing the aligned edges 43 of the skin
components 38 to create joined edges 44. This is typically achieved by
slightly overlapping aligned edges 43 and heat tacking the edges together
at spaced-apart positions along the overlapped, aligned edges 43.
Alternatively, aligned edges 43 could be placed to create butt joints
which would be temporarily secured using heat-sensitive tape.
In comparing first and second skin layers 40, 42 it is noted that joined
edges 44 of first skin layer 40 are not aligned with but are offset from
joined edges 44A of second skin layer 42. This is illustrated in FIG. 4C
in which first and second skin layers 40, 42 are overlayed on one another
with joined edges 44, 44A offset. This is very important because it
permits reinforcement elements 28, 30 from one skin layer 40, 42 to cross
over joined edges 44A, 44 of the other skin layer 42, 40 so that when the
first and second skin layers are joined to create sail body 3, any
weakness created at joined edges 44, 44A are effectively dealt with.
FIG. 5 suggests placing second skin layer 44A on top of first skin layer
44, the first skin layer being supported by a convex mold element 46, to
create a material stack 64. Various methods of laminating or otherwise
joining material stack 64 of skin layers 44, 44A can be used, such as
molding between positive and negative dies or using a single positive or
negative die and forcing the skin layers together using, for example, hot
sand, to supply heat and pressure. The temporary securement of edges 44
permits skin components 38 to shift somewhat during lamination to create
the desired three-dimensional sail body 3 shown in FIG. 7. A preferred
method is described below with reference to FIGS. 6, 6A and 6B.
Material stack 64 is positioned between upper and lower flexible pressure
sheets 66, 68 as shown in FIG. 6. Pressure sheets 66, 68 are preferably
made of a flexible, elastomeric material, such as silicone, which provides
high-friction surfaces touching outer film sides 34 of material stack 64.
Upper and lower flexible pressure sheets 66, 68 are circumscribed by upper
and lower rectangular frames 70, 72. Frames 70, 72 are mounted to upper
and lower enclosure members 74, 76. Each enclosure member 74, 76 is a
generally three-sided enclosure member with open ends 78, 80. Upper and
lower enclosure members 74, 76 carrying frames 70, 72 and flexible
pressure sheets 66, 68 therewith, are then brought together as shown in
FIG. 6A. A partial vacuum is then created within a lamination interior 82
formed between sheets 66, 68 using vacuum pump 83, thus creating a
positive lamination pressure suggested by arrows 84 in FIG. 6A. First and
second end enclosure members 86, 88 are then mounted over the open ends
78, 80 of upper and lower enclosure member 74, 76 to create a sealed
enclosure 90.
First and second end enclosure members 86, 88 each include a fan 92 and an
electric heater element 94. Fans 92 cause air or other fluids, such as
oil, within enclosure 90 to be circulated around and over the outer
surfaces 96, 98 of flexible pressure sheets 66, 68. This ensures that
flexible pressure sheets 66, 68 and material stack 64 therebetween are
quickly and uniformly heated from both sides. Because the entire outer
surfaces 96, 98 can be heated in this way, the entire material stack 64 is
heated during the entire lamination process. This helps to ensure proper
lamination. The high-friction nature of sheets 66, 68 secures first and
second skin layers 40, 42 in place, while allowing some shifting of skin
components 38, and prevents any substantial shrinkage of the skin layers
during lamination. Any shrinkage which does occur should occur in all
directions to minimize any resulting crimp in any fibrous segments. After
a sufficient heating period, the interior 100 of enclosure 90 can be
vented to the atmosphere and cooled with or without the use of fans 92 or
additional fans. After being properly cooled, sail body 3 is removed from
between pressure sheets 66, 68; see FIG. 7. Sail body 3 is finished in
customary ways to create sail 2.
FIGS. 6, 6A and illustrate the perforated nature of mold element 46A
contacting outer surface 98 of lower flexible pressure sheet 68. In the
preferred embodiment, perforated mold element 46A is made up of a number
of relatively thin vertically-oriented members 104 oriented parallel to
one another with substantial gaps therebetween to permit the relatively
free access to the heated fluid to lower surface 98. Preferably, no more
than about 20%, and more preferably no more than about 5%, of that portion
of lower surface 98 which is coextensive with material stack 64 is covered
or effectively obstructed by perforated mold element 46A. Instead of
vertically-oriented members 104, perforated mold element 46A could be made
of, for example, honeycomb with vertically-oriented openings. Many dead
spaces could be created within the vertically-extending honeycomb
channels, thus substantially hindering heat flow to large portions of
lower surface 98. This can be remedied by, for example, changing the air
flow direction so the air is directed into the honeycomb channels,
minimizing the height of the honeycomb, and providing air flow escape
channels in the honeycomb near surface 98. Other shapes and configurations
for perforated mold element 46A can also be used.
Preferably the heated fluid within interior 100, which may be a gas or a
liquid, is in direct thermal contact with upper and lower surfaces 96, 98.
However, in some circumstances an interposing surface could be created
between the heated fluid and surfaces 96, 98. So long as such interposing
surfaces do not create a significant heat barrier, the heated fluid will
remain in effective thermal contact with outer surfaces 96, 98 of pressure
sheets 66, 68.
Modification and variation can be made to the disclosed embodiments without
departing from the subject of the invention defined by the following
claims. For example, first and second skin layers 40, 42 may be made of
the same or different materials. One or both films 22 may not be
imperforate. First and second skin layers 40, 42 are congruent--they have
the same shape and size; they could be of slightly different sizes (such
as to permit the peripheral edge of one to be folded over the peripheral
edge of the other during finishing operations) and yet be effectively
congruent.
Any and all patents, patent applications and printed publications referred
to above are incorporated by reference.
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